Due to the proliferation of personal computers, the widespread acceptance of the Internet, and the advent of the Information Age, there is a virtual explosion in the amount of digital data transmissions. Currently, one common method for transmitting and receiving digital data involves the use of telephone modems. A telephone modem is used to transmit digital data generated by a computer to an intended destination over standard telephone lines. The same modem also can receive digital data from a telephone line. This setup enables computers to gain access to the Internet and other on-line services over standard telephone jacks. Although this form of communications is convenient, it is painfully slow because telephone lines simply consist of pairs of twisted copper wires. These lines were primarily designed to carry analog voice signals rather than digital data. As such, telephone lines are bandwidth limited, and the rate at which digital data can be transmitted is relatively quite slow. It can take several minutes or even hours to download picture, audio, and video files via standard telephone modems. Hence, telephone modems are not ideally suited for conveying video (e.g., teleconferencing, movies, etc.), graphics (e.g., computer-aided design, medical imaging, simulations), or multimedia applications.
A faster medium for high-speed communications entails the use of dedicated computer networks, whereby computers are interconnected to form local area networks or wide area networks (LAN/WAN). However, the downside to this approach is the high cost of purchasing, routing, and maintaining the requisite interconnecting coaxial and fiber lines. Furthermore, highly skilled network administrators are necessary to monitor the network in order to keep it operational. In addition, expensive networking equipment (e.g., routers, hubs, repeaters, concentrators, servers, bridges, etc.) must be purchased and installed. Hence, the advantage of having faster data communications and higher bandwidth comes at a steep price. Furthermore, it is prohibitively expensive to set up dedicated computer networks amongst individual homes.
There is, however, another medium which is widespread and already in place and which also has a very high bandwidth suitable for transmitting vast amounts of information. This medium is the cable TV (CATV) networks. CATV is comprised of coaxial and fiber optic cables which have very high transmission capacity. These CATV lines connect a central station or headend to set-top boxes in everyone's homes. In the past, CATV was primarily limited to being a one-way only transmission medium. Rather than transmitting TV signals through the airwaves, the TV signals were distributed from the headend terminal, over the CATV network, to a host of subscriber units. After down conversion, the RF TV signals are eventually input to a subscriber's television set. However, instead of simply broadcasting TV signals, it is feasible to use these same CATV networks to provide high capacity two-way data communications. In fact, developers have been working on systems for delivering various digital data over standard CATV networks. By using a cable modem coupled to the CATV network, computers can transmit and receive packet data much more quickly.
There are several problems which must be overcome in order to successfully commercialize two-way data communications over a CATV network. One of the problems encountered with utilizing CATV as a data highway is due to the fact that there is a wide proliferation of different data formats, rates, and requirements. On the one hand, digital files are often sent by means of packetizing the data and independently routing the packet data according to a widely accepted Ethernet protocol. In contrast, internet traffic is handled according to a specific Internet protocol (IP). Also, digital video adheres to an industry standard Motion Pictures Experts Group (MPEG) format. And there are well established telephony standards as well. Each of these formats were developed for accomplishing a specific task and is not readily suitable for other uses. For example, the Ethernet protocol efficiently routes individual packet data to their respective destinations. Although it is possible to digitize audio and video signals and transmit the data as Ethernet packets over CATV, there may be significant delays incurred while awaiting the arrival of the data packets. Hence, it would be difficult to transmit live video or hold telephone conversations via Ethernet. Likewise, it would be extremely difficult and inefficient to transmit data files via the MPEG standard.
Another problem relates to the fact that some data transmissions are extremely delay sensitive, whereas other data might not be as time critical. For example, telephone communications requires that the corresponding data be transmitted rapidly so that the parties can carry on conversations with imperceptible lags. The same holds true for video teleconferencing. In contrast, Internet data can be routed as bandwidth permits because users can suffer slight delays in receiving the data for display and in the transmission of IP datagrams. Other problems arise due to the unique situation whereby there is a single headend controller servicing a multitude of cable modems. The headend controller must transmit in a one-to-many mode. Conversely, the cable modems must transmit in a many-to-one configuration. Identifying and routing which signals are to be sent to one or more specific cable modems is quite challenging. Likewise, allocating bandwidth and resources to handle the multitudes of cable modem transmissions can be overwhelming.
The present invention overcomes these problems by applying a cell-based Asynchronous Transfer Mode (ATM) approach to CATV networks. The selection of ATM cells as the data-link layer protocol has several advantages. First, it is capable of supporting services requiring real-time functionality (e.g., full-duplex voice communications, video teleconferencing, etc.). At the same time, it is also well suited for handling data transmissions which are not as delay sensitive (e.g., Internet services). In addition, the nature of an ATM cell based system allows for other multimedia applications to be upgraded without requiring iterative changes to the underlying structure. With the present invention, packet data in various formats are converted into ATM cells and transmitted in a shared radio frequency spectrum over standard cable TV networks. Virtual connections are exploited to appropriately prioritize and route individual cells. Hence, the present invention offers a flexible, effective, economic, and fully integrated multimedia bearer system granting immediate support for Internet services, traditional voice telephony, and digital video services.